This invention relates to optical detection systems using a plurality of sensors, each of which is sensitive to radiation in a different band of the optical spectrum.
Optical detection systems which must scan large unknown areas at rapid rates of speed or which must scan remote electromagnetic radiation sources in general have difficulty in discriminating between radiation emitted by the object it is desired to locate and incidental, or ambient radiation. One such system is carried on-board aircraft or sea-going vessels to detect the flash of firing anti-aircraft guns, missiles or fuzes. As the detectors of this system scan the ground or sea, ambient light is often reflected and the detectors will give false positive readings. Another such system with similar difficulties is one used to remotely sense temperature. In this system solar radiation may cause erroneous measurements. The reason for this difficulty and one method of overcoming it will become more understandable on an examination of some fundamentals of electro-optics.
The optical spectrum includes electromagnetic radiation which varies from UV radiation, through the visible spectrum, to IR radiation. The radiation of the optical spectrum has wave lengths which vary from less than 0.35 micrometers to greater than 14 micrometers.
A radiating source of electromagnetic energy, such as a gun flash, does not radiate at a single wave length, but rather emits at a series of wave lengths of varying intensities, which is called its optical "signature." Thus, a radiating source such as a gun flash may have an optical signature which is different from that of other sources.
One means of discriminating between spurious radiation and the radiation it is desired to detect is to use two detectors, each of which detects the radiation in a different, narrow band of the spectrum. By careful selection of the bands of radiation detected, the outputs of the detectors may be compared against known outputs to determine whether the radiation detected has the signature of the radiation it is desired to detect.
The major difficulties with this two detector system are its directionality and its complicated, lens type construction. When flashes of light impinge on the detectors at angles which deviate from an axis perpendicular to the plane of the two detectors, one of the two detectors may fail to detect this flash. The result will be inaccurate data obtained from the detector system. In addition, the complicated lens-type arrangement increases the risk that components of the system will be injured when subjected to shock or will become misaligned during normal use. The present invention has been made in order to eliminate these difficulties.